HIV infection requires the integration of a DNA copy of the viral genome into the host DNA. Therefore therapeutic strategies to prevent HIV DNA integration are essential to block HIV infection. The role of cellular factors in this viral process is poorly defined. The Lens Epithelium-Derived Growth Factor p75 (LEDGF/p75) is a well characterized cellular cofactor of HIV DNA integration. However, it remains unexplained why Lentiviruses have evolved dependency of this cellular protein for efficient viral DNA integration. Work from my group and others have determined that LEDGF/p75 tethers the HIV integration complex to the host chromatin. However, this mechanism does not explain the strategies used by the chromatin-bound HIV pre-integration complex to gain access to the host DNA, a necessary step for integration to the host DNA, or to exploit further the cellular DNA repair machinery to promote post-integration DNA repair. New findings from my laboratory provide potential molecular explanations for these essential aspects of the HIV DNA integration process. We have demonstrated for the first time the existence of several protein motifs in LEDGF/p75 necessary for the HIV DNA integration in a chromatin tethering-independent manner. These motifs contain residues that are phosphorylated or SUMOylated, or that are predicted to be part of protein-protein interaction modules. We have postulated that these LEDGF/p75 motifs are involved in recruiting cellular proteins implicated in the HIV DNA integration process. In further support of this model, our laboratory has identified novel LEDGF/p75- interacting proteins known to be involved in chromatin remodeling, DNA repair, and transcriptional elongation. In summary, our model postulate that Lentiviruses have evolved LEDGF/p75-dependency for optimal HIV DNA integration because this cellular protein: (i) tethers the HIV pre-integration complex to subregions of the chromatin engaged in active transcription, and (ii) provides to the virus, through LEDGF/p75-specific protein- protein interactions, access to the host DNA and to DNA repair mechanisms particularly active in actively transcribe DNA. In addition, we postulate that some LEDGF/p75-interacting proteins will impair the HIV cofactor activity of this protein. In this proposal we will demonstrate essential aspects of this novel model. Specifically we will: (i) Define the role in HIV DNA integration of LEDGF/p75-interacting proteins implicated in DNA repair and chromatin remodeling. (ii) Determine the functional implications in HIV DNA integration of LEDGF/p75 motifs involved in post-translational modifications and protein-protein interactions. (iii) Provide further support to our model by determining genome-wide the correlation between LEDGF/p75 location and HIV DNA integration site selection.